The production of phenol and/or cyclohexanone from cyclohexylbenzene is an emerging technology, interesting in that it co-produces cyclohexanone, rather than acetone. Cyclohexylbenzene may be produced, for example, by direct alkylation of benzene with cyclohexene, or as disclosed in U.S. Pat. No. 6,037,513, by contacting benzene with hydrogen in the presence of a catalyst. The cyclohexylbenzene may then be oxidized to the corresponding hydroperoxide and the hydroperoxide cleaved to phenol and cyclohexanone using a catalyst. Depending upon need or demand, the phenol and cyclohexanone may each be taken as products, and/or the phenol can be hydrogenated to produce additional cyclohexanone, and/or the cyclohexanone can be dehydrogenated to produce additional phenol. Cyclohexanone is widely used to make caprolactam, which, in turn, is used for making nylon-6, a widely used polymer material. Phenol may be used to make a wide variety of chemical products, including bis-phenol A, polycarbonates, phenolic resins, and the like.
In such processes for the co-production of phenol and cyclohexanone, the oxidation of cyclohexylbenzene to cyclohexylbenzene hydroperoxide may be a gas-liquid oxidation that takes place through a free radical chain reaction catalyzed by an N-hydroxy-substituted cyclic imide, such as N-hydroxyphthalimide (NHPI), for instance as described in WO 2014/137623. In particular, a cyclohexylbenzene-containing liquid and an O2-containing gas (such as pure O2, air, and diluted air and O2) may be supplied into an oxidation reactor, where they are allowed to contact each other, such that the cyclohexylbenzene is oxidized by O2 molecules either at the gas-liquid interface and/or in the liquid phase. Inside the liquid reaction medium, along with the desired oxidation route which forms cyclohexyl-1-phenyl-1-hydroperoxide (hereinafter “1-CHB-HP), a number of side reactions may occur simultaneously producing various undesirable byproducts. It has been found that both the conversion of cyclohexylbenzene and selectivity toward 1-CHB-HP is highly dependent on the temperature of the reaction medium. Also, if temperature in a hot spot rises to an exceedingly high level, the hydroperoxide product may decompose. Due to the exothermic nature of the oxidation reactions, temperature non-uniformity inside the liquid reaction medium may occur, especially during periods of process upset where agitation produced by the O2-containing gas supplied into the reactor body is reduced, leading to the formation of undesirable levels of byproducts and potentially unsafe reaction conditions.
Thus, careful design of the oxidation process and oxidation reactor is needed to reduce undesirable side reactions and the formation of byproducts.